Stages of cancer

"Staging" of cancer is a means to help categorize the severity of the disease, establish a prognosis for the individual, and determine a recommended treatment for the condition based on the location and severity of the disease.

A current standard format for staging includes the TMN classification. "T" refers to the size or location of the tumour at its original (or "primary") site, and whether it has extended to local tissue. "N" refers to the involvement of any lymph nodes. "M" refers to the presence of tumour cells in more distant metastatic sites.

Alternatively, a four-staged, Roman numeral classification is often used. The stages in this system reflect the extensiveness of the cancer, with Stage I being the least extensive and Stage IV being the most extensive. Colon cancer uses a "Duke's" classification with the earliest stage term "Duke's A" and the most advanced being a "Duke's D". Using these forms of staging does not preclude also categorizing cancer in the TMN classification.

Additionally, cancers can be categorized as to how closely they resemble the original tissue from the primary site. "Well differentiated" cancers resemble the original tissue fairly closely and are considered less severe. "Moderately differentiated" tissues are intermediate in severity and "poorly differentiated" cancers indicate a more serious and aggressive disease. Prostate cancer uses a "Gleason" scale to characterize the differentiation of the cells with higher numbers indicating more poorly differentiated cancers.